The present invention relates in general to magnetic stereo phonograph cartridges and, more particularly, it relates to such cartridges having a separate and replaceable stylus assembly.
As is well known, stereophonic phonograph records includes two sound tracks in the record groove which are mutually perpendicular to each other. In coordinate terms, the two tracks can be referred to as an x track and a y track. The stylus rides in the groove moving simultaneously as a function of the x and y tracks and, since the stylus cantilever is pivoted, an armature connected to it describes a corresponding motion at the end thereof opposed to the stylus. Functionally, x motion is between (or adjacent) a first pair of spaced pole pieces of a first electromagnet circuit and y motion is between (or adjacent) a second pair of spaced pole pieces of a second electromagnet circuit. As the armature is magnetized, voltages proportional to the x and y signals are induced in the respective circuits. While it would be convenient to visualize the x and y motions as horizontal and vertical, resulting from tracks on the bottom and one side of a three-sided groove, this so-called 0/90 system has never found commercial favor. Rather, today's stereophonic records have the tracks located on either side of a two-sided 90.degree. groove, called, with reference to the vertical axis of the groove and the stylus, the 45/45 system. Operation is in precisely the same mode, but for the electromagnet circuits to generate signals responsive to each track, the two opposed pairs of pole faces must also be at the same 45.degree. angle to the vertical axis.
Those familiar with the art will appreciate that any initial deviation by the armature from absolute dead center with respect to the four pole pieces is going to produce a distorted signal. What is perhaps not so apparent is that the dead-center positioning is only required when the tone arm is resting on a record, e.g. when a force equal to the tracking weight of the arm has already pivoted the stylus in the vertical direction. What is even less apparent is that in prior art devices the armature-energizing magnet was so positioned that it also acted to pull the armature from a dead-center position. Further, any mis-alignment of the stylus tip from the vertical will also produce a distorted signal and, while this is well recognized, convenient means for achieving it, or correcting a mis-alignment, have been lacking.
With respect to prior art, of which there is a substantial body, my own U.S. Pat. No. 3,294,405 may be considered typical. Alignment of the stylus assembly and the housing is there provided by ridges on the former and grooves on the later, the whole being retained by a pair of mounting screws. A rectangular elastomeric pivot block retains the armature-stylus (cantilever) assembly.